1. Field of the invention:
This invention relates to a semiconductor laser device with a structure by which the rise of the temperature of the facets that is caused by the light absorption of the facets can be prevented, thereby attaining stabilized laser oscillation for a long period of time even at high output power.
2. Description of the prior art:
Semiconductor laser devices that can oscillate coherent light have been used as light sources in optical disc apparatuses, optical communication systems, etc. As optical disc apparatuses, there have been add-on-memory type optical disc apparatuses that achieve writing operation and erasable memory type optical disc apparatuses that achieve erasable operation. Semiconductor laser devices that are used as light sources in these optical disc apparatuses are required to produce optical output power as high as 20-40 mW. For this purpose, in recent years, high output power semiconductor laser devices have been put into practice. The high output power semiconductor laser devices are disadvantageous in that the light-emitting facet thereof tends to deteriorate. It has been reported that high output power semiconductor laser devices oscillating laser light at high output power deteriorate in inverse proportion to the fourth power of the optical output in the cases where semiconductor laser devices with the same structure are examined.
FIG. 6 shows a conventional VSIS (V-channeled substrate inner stripe) semiconductor laser device, which is produced as follows: On a p-GaAs substrate 11, an n-GaAs current blocking layer 12 is formed. Then, a V-channel with a width W1 is formed on the current blocking layer 12 in such a manner that the V-channel reaches the substrate 11 through the current blocking layer 12. On the current blocking layer 12 including the V-channel, a p-GaAlAs cladding layer 13, a GaAs or GaAlAs active layer 14, an n-GaAlAs cladding layer 15, and an n-GaAs cap layer 16 are successively formed. Current for laser oscillation is confined by the n-GaAs current blocking layer 12 and only flows into the channel with a width W1. Laser light that is produced in the active layer 14 is absorbed by the n-GaAs current blocking layer 12 that is positioned outside of the V-channel, so that a difference arises in the effective refractive index between the portion of the active layer 14 corresponding to the V-channel and the other portions of the active layer 14 corresponding to the outside of the V-channel, resulting in an optical waveguide in the active layer 14. Thus, laser oscillation can be attained in a stabilized fundamental transverse mode. The said waveguiding structure functions as a loss-waveguide structure. This VSIS laser device is disadvantageous in that although it can attain laser oscillation in a stabilized fundamental transverse mode at a low output power level, it cannot continue to oscillate laser light for a long period of time at a high output power level with extreme reliability. The reasons why the above-mentioned laser device deteriorates at a high output power level are based on the deterioration of the shoulders of the V-channel in the vicinity of the facets, which is caused by heat generation of the n-GaAs current blocking layer 12 corresponding to the shoulder portions of the V-channel that absorbs light that leaks from the optical waveguide. The diffusion length of the minority carrier within the n-GaAs current blocking layer 12 is short, so that the carrier that is produced by the light absorption achieves a non-radiative recombination in the vicinity of the shoulder portions of the V-channel, resulting in the generation of heat.